The recoil properties of the lung and other elastic tissues are due largely to elastic fibers. These complex structures consist of two morphologically distinguishable components: the protein elastin, and 10-12 nm microfibrils, which contain the structural proteins fibrillin, MAGP-1, and, perhaps, several others. In many diseases, disorganized elastic fibers lead to alterations in tissue integrity and compromised mechanical function. While technical advances in molecular biology have given us new information about elastin gene expression and elastin synthesis, surprisingly little is known about how the elastic fiber is assembled at the molecular level. During the past funding period, we have addressed the problem of elastic fiber assembly by systematically evaluating domains on elastin and microfibrillar proteins to ascertain their role in mediating protein-protein interactions. The results of our study suggest that the assembly of elastin into a fibrillar matrix is a complex stepwise process that involves interactions between elastin molecules and molecules of the microfibrillar network. In this application, we will investigate the possibility that microfibrils serve to nucleate or instigate elastin assembly, but that once started, elastin self-assembles onto the expanding elastin core to form a larger polymer. Our specific aims focus on: 1) Characterizing sequences within tropoelastin that mediate its association with microfibrils and promote self-assembly; 2) Elucidating domains within the fibrillin molecule responsible for assembly into a microfibril; 3) Using transgenic mice to study the process of elastic fiber assembly in vivo. Not only will the results of this study help us understand elastin assembly at a molecular level, but they are also fundamentallyimportantin understandinginherited and degenerative diseases that involve the elastic fiber.